NavList:

I don't think anyone has mentioned the direct computation approach to this. It's in the Nautical Almanac in some form, but suppose you just want some minimalist instructions to go from the sextant sight Hs to the corresponding Ho (after which it no longer matters that it's a Moon sight; you process it however you wish to yield latitude, longitude, or a celestial line of position).

Somewhere offshore near southern New England, at 12:07:16 UT today (19 Oct 2024), I observe the altitude of the Moon's Upper Limb: 18°57'. I have no index correction. My height of eye is 3.1 meters (10 feet). Air temp is 8°C and pressure is 1035 mb. I'll spare you an almanac lookup and specify that the HP of the Moon at this time is 60.4'. What are the steps to get the Ho using only simple calculator equations? Note: I have specified this as a UL sight so that it might have been taken with a marine sextant, and you have to calculate the SD to get it right. What steps would be changed or ignored for a bubble horizon sight?

Are there any special cases that are not covered by this example? Should we worry about those, or just mark them as "off limits"? What corrections can be ignored if we're working in the +/-1' precision range and no better?

Frank Reed